1. Technical Field
The present disclosure relates to an ink supply control method of an inkjet printer that pressurizes an elastic ink pack with a pressure pump and supplies ink from the ink pack to an ink path that communicates with an inkjet head, and to an inkjet printer.
The present application is a continuation application of U.S. patent application Ser. No. 14/051,961, filed on Oct. 11, 2013, which is scheduled to issue on May 19, 2015 as U.S. Pat. No. 9,033,475. The present application claims priority based on and incorporates by reference the entire contents of Japan Patent Application No. 2012-225748 filed in Japan on 2012 Oct. 11,and Japan Patent Application No. 2012-226677 filed on 2012 Oct. 12.
2. Related Art
An inkjet printer according to the related art is described in Japanese Unexamined Patent Appl. Pub. JP-A-2009-190410. An ink cartridge used in the inkjet printer disclosed in JP-A-2009-190410 has an elastic ink pack that holds ink, a rigid case that holds the ink pack, and a pressure chamber formed between the case and the ink pack. The inkjet printer applies pressure to the ink pack by feeding air into the pressure chamber by means of a pressure pump, and pressure feeds ink from the ink pack into the ink path.
The pressure pump used in JP-A-2009-190410 has a pressure sensor for detecting the pump pressure. The pressure sensor has an intake chamber to which air fed from the pump unit to the pressure chamber is introduced, a diaphragm that is a wall of the intake chamber and is displaced by the pressure inside the intake chamber, and an optical sensor unit that detects displacement of the diaphragm. When the diaphragm is detected by the optical sensor unit to have displaced to a position pushed to the outside of the intake chamber, the pressure sensor detects that the pressure of the pressure pump is at a first pressure sufficient to pump ink through the ink path. When the diaphragm is detected by the optical sensor unit to have displaced to a position collapsed to the inside of the intake chamber, the pressure sensor detects that the pressure of the pressure pump is at a second pressure, which is lower than the first pressure.
The pressure of the pressure pump drops over time. The pressure of the pressure pump also drops with consumption of ink by the inkjet head, that is, as the amount of ink in the ink pack decreases. Because ink in the ink pack cannot be supplied to the ink path when the pressure of the pressure pump drops enough, the inkjet printer disclosed in JP-A-2009-190410 drives the pressure pump and pumps air into the pressure chamber when the pressure of the pressure pump is detected to have dropped to the second pressure.
The pressure applied to the ink pack to feed ink into the ink path (that is, the pressure of the pressure pump) is set so that the first pressure, which is the sum of the ink meniscus pressure formed in an ink nozzle of the inkjet head and the pressure of the pressure pump, is greater than the second pressure, which is the sum of the potential head of the ink pack, the back pressure of the ink pack, and the dynamic pressure of the ink path.
The back pressure of the ink pack rises rapidly when little ink is left in the ink pack. Therefore, when the pressure pump is set to a low pressure, ink inside the ink pack cannot be sufficiently pumped into the ink path, and the amount of ink left in the ink pack instead of being pumped into the ink path increases. However, if the pressure pump is set to a high pressure, the amount of residual ink can be decreased but the service life of the pressure pump is shortened because the drive time of the pressure pump is increased.
When print data is not supplied to the inkjet printer from an external device for a certain period of time, control may go to a power conservation mode that stops supplying power to the motors and sensors and provides power only to the CPU or other control unit. If the pressure of the pressure pump is managed based only on output from the pressure sensor in this type of inkjet printer, the pressure of the pressure pump cannot be determined while in the power conservation mode. For example, if operation continues in the power conservation mode for an extended time, the pressure of the pressure pump may drop below the second pressure over time. However, because there is no output from the pressure sensor while in the power conservation mode, the control unit cannot determine the pressure in the pressure pump. Because driving the pressure pump cannot be controlled based on output from the pressure sensor, keeping the pressure of the pressure pump above the second pressure level during the power conservation mode is difficult.
If print data is supplied from an external device while the inkjet printer is in the power conservation mode, the inkjet printer must exit the standby mode and resume the normal operating mode. Once the normal operating mode is resumed, the inkjet printer drives the pressure pump until the first pressure is reached so that ink can be pumped from the ink pack into the ink path, and then starts printing the print data. If the pressure of the pressure pump is significantly below the second pressure at this time, the pressure pump must be driven a long time to reach the first pressure, and the delay between receiving the print data and starting to print the print data increases.